Focused particle beam systems and methods using a tilt column

ABSTRACT

Particle beam systems and methods for interacting with a workpiece according to this invention include a work stage assembly and a first particle beam source. The work stage assembly is adapted a) for supporting a workpiece, b) for translating along a first axis, c) for translating along a second axis perpendicular to the first axis, and d) for rotating about a third axis perpendicular to both the first axis and the second axis. The work stage assembly has a work stage axis substantially parallel to the third axis. The first particle beam source for interacting with the workpiece is supported by the work stage assembly. The first particle beam source has a first particle beam axis. In one embodiment, the first particle beam source is oriented so that the first particle beam axis forms an angle with the third axis. In another embodiment, the first particle beam source is tiltable from a first position, with the first particle beam axis substantially parallel to the third axis, to a second position, with the first particle beam axis forming an angle with the third axis. Thus, the particle beam system can etch and image a vertical cross-section of the workpiece without offsetting the work stage axis from the third axis.

BACKGROUND OF THE INVENTION

The present invention relates to focused particle beam systems andmethods for processing a workpiece, e.g., etching and imaging across-section of a workpiece.

Present focused ion beam (FIB) systems typically include an ion beamcolumn oriented normal to the workpiece and a tilting work stage. Suchsystems can include an electron column offset from the normal to theworkpiece. To image a cross-section of a workpiece using an ion column,existing systems etch a cavity in the workpiece and tilt the stage sothat the ion beam can impinge on a side wall of the cavity.

Existing FIB systems which incorporate a tilting stage experienceseveral problems. A tilting work stage, which is large relative to manyof the other components of a FIB system, causes the system to berelatively bulky. Such a large bulk is disadvantageous because cleanroomfabrication space is expensive. A tilting work stage also causes an FIBsystem to be unstable because a tilting work stage can make an FIBsystem susceptible to low frequency vibration and gravity sag, asdiscussed further below. Disadvantageously, the vibration of and thechanging configuration of a tilting work stage can interfere with theperformance of a system component, such as a laser interferometer. Laserinterferometry can be used to assist in accurate monitoring of theposition of a workpiece.

Low frequency vibration can occur when a massive object, such as atilting stage, is supported by bearings and held steady with a mechanismthat behaves like a spring. Low frequency vibration reduces resolutionof a focused particle beam system by adding uncertainty in thedetermination of the location of the target point, i.e., where the ionbeam interacts with the workpiece.

When a large work stage assembly is tilted, gravity can bend componentsof the work stage assembly and the workpiece. Such bending is termedgravity sag. It is difficult to monitor gravity sag. Thus, gravity sagcan lead to inaccuracy in determining the positions of the work stageand of the workpiece. Such inaccuracy can reduce the resolution of afocused particle beam system.

Existing configurations of FIB systems restrict access to the workpieceby other elements, such as an optical microscope. Further, existingsystems do not allow for optimization of the working distance ofparticular ion and electron columns. In existing configurations with afocused ion beam oriented normal to the workpiece and an electron beamoffset with respect to the normal, one can not achieve working distancesthat optimize the characteristics, e.g., resolution and current density,of the ion and electron beams, because the work stage and the tip of theion column and the tip of the electron column physically interfere witheach other.

Accordingly, it is an object of the present invention to provideimproved focused particle beam systems and methods for processing, e.g.,etching and imaging a cross-section of a workpiece.

It is another object of the invention to reduce the footprint of afocused particle beam system.

It is another object of the invention to improve the stability of thework stage assembly of a focused particle beam system.

It is another object of the invention to improve the accuracy of afocused particle beam system.

It is another object of the invention to provide a focused particle beamsystem that allows for concurrent optimization of the working distancesof a particle beam column and an electron beam column, the columns beingoriented so that their target points are substantially coincident.

It is another object of the invention to provide a focused particle beamsystem that allows greater access to the workpiece by additional systemelements such as an optical microscope.

Other objects of the invention will in part be obvious and in part willappear hereinafter.

SUMMARY OF THE INVENTION

One version of a particle beam system for interacting with a workpieceaccording to this invention, has a housing and an element for processinga workpiece contained in the housing. The processing element includes awork stage assembly and a first particle beam source. The work stageassembly is adapted a) for supporting the workpiece, b) for translatingthe workpiece along a first axis, c) for translating the workpiece alonga second axis perpendicular to the first axis, and d) for rotating theworkpiece about a third axis perpendicular to both the first axis andthe second axis. The work stage assembly has a work stage axissubstantially parallel to the third axis.

The first particle beam source interacts with the workpiece supported bythe work stage assembly. The first particle beam source is located abovethe work stage assembly and has a first particle beam axis. The firstparticle beam source is oriented so that the first particle beam axisforms an acute angle with the third axis. Thus, the particle beam systemcan etch and image a vertical cross-section of the workpiece withoutoffsetting the work stage axis from the third axis.

Workpieces or samples, such as wafers containing semiconductor devices,can contain features or structures having aspect ratios of 15:1. Thus,when cross-sectioning and imaging the cross-section of a workpiececontaining such features or structures, the cross-section should besufficiently vertical such that an individual feature's aspect ratio isaccurately reflected in the cross-section.

Further, for the purposes of this application, one axis is defined asoffset relative to another axis when the one axis forms an acute anglewith respect to the other axis.

For illustration purposes only, and not to be taken in a limiting sense,the above-mentioned first and second axes can define a horizontal planeand the above-mentioned third axis can be a vertical axis. In this case,the work stage assembly can be adapted a) for supporting the workpiecein a horizontal plane, b) for translating the workpiece along aforward/backward direction, c) for translating the workpiece along aside to side or along a right/left direction, and d) for rotating theworkpiece about the vertical axis. The work stage assembly has a workstage axis substantially parallel to the vertical axis. The firstparticle beam source has a first particle beam source axis oriented toform an acute angle with the vertical axis. Thus the particle beamsystem can etch and image a vertical cross-section of the workpiecewithout offsetting the work stage axis from the vertical axis.

There are several embodiments of this version of a focused particle beamsystem according to the invention. The first particle beam axis can forman angle of about forty-five degrees with the third axis. The system canfurther include a second particle beam source for interacting with theworkpiece, located above the work stage assembly. The second particlebeam source can have a second particle beam axis. In one embodiment, thesecond particle beam source is oriented so that the second particle beamaxis is substantially parallel to the third axis. In another embodiment,the second particle beam source is oriented so that the second particlebeam axis is offset relative to the third axis.

In another embodiment, the system can further include an electron beamsource for interacting with the workpiece. The electron beam source islocated above the work stage assembly and has an electron beam axis. Theelectron beam source is oriented so that the electron beam axis isselectively offset relative to the third axis.

There are still other embodiments of this version of a focused particlebeam system according to the invention. The system can be configured sothat the first particle beam axis and the electron beam axis each forman angle of about forty-five degrees with the third axis. Further, thesystem can be configured so that the first particle beam axis and thethird axis form a first plane and the electron beam axis and the thirdaxis form a second plane substantially perpendicular to the first plane.This system configuration is advantageous because the system can etch avertical cross-section of a workpiece using the first focused particlebeam source and can image the vertical cross-section using the electronbeam without rotating the workpiece.

The system can be configured so that the work stage assembly includes alaser interferometer element for assisting in the accurate determinationof the position of the workpiece. The laser interferometer can include alaser source, a beam splitter, at least one reference mirror, and atleast one test mirror. The laser source directs laser radiation along apath in a first direction. The beam splitter is located in the path ofthe laser radiation from the laser source and transmits a first part ofthe laser radiation along the first direction, and reflects a secondpart of the laser radiation along a second direction. The referencemirror reflects back to the beam splitter the first transmitted part ofthe laser radiation. The test mirror reflects back to the beam splitterthe second reflected part of the laser radiation and is located on saidwork stage assembly. Thus, the beam splitter combines the firsttransmitted part and the second reflected part of the laser radiation toform interference fringes that assist in the determination of theposition of the workpiece.

The system can also be configured to include a gas injection source oran optical microscope or both. The gas injection source typically has agas injection nozzle located above and in selected proximity to theworkpiece. The optical microscope has an optical microscope axis and isoriented so that the optical microscope axis is substantially parallelto the third axis. One can use the optical microscope for so-calledtop-down wafer navigation.

The system can also be configured to include a work stage assembly thatrotates more than twenty- five degrees, more preferably at leastforty-five degrees and most preferably at least ninety degrees.

According to another version of the invention, the first particle beamsource for interacting with the workpiece is tiltable from a firstposition, where the first particle beam axis is substantially parallelto the third axis, to a second position, where the first particle beamaxis forms an angle with the third axis. With this arrangement, theparticle beam system can etch and image a vertical cross-section of theworkpiece without offsetting the work stage axis from the third axis.

A method for using a particle beam system to interact with a workpiece,according to one version of the invention, includes the steps of a)providing a particle beam system, b) placing the workpiece on a workstage assembly, and c) etching with the focused particle beam source afirst cavity in the workpiece to expose at least a portion of at leastone structure contained in a vertical cross-section of the workpiece.

The step of providing the particle beam system can include providing awork stage assembly adapted a) for supporting a workpiece, b) fortranslating the workpiece along a first axis, c) for translating theworkpiece along a second axis perpendicular to the first axis, and d)for rotating the workpiece about a third axis perpendicular to both thefirst axis and the second axis. The work stage assembly has a work stageaxis substantially parallel to the third axis.

The step of providing the particle beam system can also includeproviding a first particle beam source for interacting with theworkpiece. The first particle beam source is located above the workstage assembly. The first particle beam source has a first particle beamaxis. The first particle beam source is oriented so that the firstparticle beam axis forms an acute angle with the third axis.

Thus, the particle beam system can etch and image a verticalcross-section of the workpiece without offsetting the work stage axisfrom the third axis.

The step of providing a particle beam system can further include thestep of providing an electron beam source for interacting with theworkpiece. In this embodiment, the electron beam source is located abovethe work stage assembly and has an electron beam axis. The electron beamsource is oriented so that the electron beam axis is selectively offsetrelative to the third axis.

The step of providing a particle beam system can further include thestep of providing the electron beam source and the first particle beamsource with the first particle beam axis and the electron beam axis eachforming an angle of about forty-five degrees with the third axis.Further, the first particle beam axis and the third axis can form afirst plane and the electron beam axis and the third axis can form asecond plane such that the first plane is substantially perpendicular tothe second plane.

The above method can further include the step of imaging the verticalcross-section of the workpiece using the electron beam source.

The above method can further include the step of etching a second cavityin selected proximity to the first cavity so as to produce atransmission electron microscope (TEM) sample wall or lamella separatingthe two cavities. The TEM lamella can have first and second opposedsides. The first side faces the first cavity and the second side facesthe second cavity. The method can further include the steps ofbombarding the second side of the TEM lamella with electrons from theelectron gun, and monitoring the change in secondary particle emissionfrom the lamella while etching the second cavity to monitor thethickness of the lamella.

The method described above can further include the step of rotating theworkpiece ninety degrees about the third axis to expose the verticalcross section to the first particle beam source subsequent to theetching step. Subsequent to the rotating step, the focused particle beamsystem can image the vertical cross-section of the workpiece using thefocused particle beam source.

Another version of a particle beam system for interacting with aworkpiece according to the invention includes a work stage assembly forsupporting a workpiece and for orienting the workpiece in a plane. Thework stage assembly has a support element adapted for translating theworkpiece along a first axis, and for translating the workpiece along asecond axis perpendicular to the first axis. The support element has afirst side and a second side, and a positioning assembly coupled to thefirst side of the support element and adapted for rotating the supportelement and the workpiece about a third axis perpendicular to both thefirst axis and the second axis, such that the workpiece can be seated onthe second side of the support element and translated in a plane androtated about the third axis normal to that plane.

The system further includes a first particle beam source for interactingwith the workpiece. The workpiece is supported by the work stageassembly. The first particle beam source is located above the work stageassembly and has a first particle beam axis. The first particle beamsource is tiltable from a first position with the first particle beamaxis substantially parallel to the third axis, to a second position withthe first particle beam axis forming an acute angle with the third axis.Thus, the particle beam system can etch and image a verticalcross-section of the workpiece without tilting the work stage axisrelative to the third axis.

These and other features of the invention are more fully set forth withreference to the following detailed description and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective schematic view of one embodiment of a particlebeam system according to the invention;

FIG. 2 is a schematic illustration of an alternative embodiment of aparticle beam system according to the invention;

FIG. 3A shows a cross sectional view of a workpiece undergoing 45 degreemilling by the particle beam source of FIG. 1;

FIG. 3B is a perspective view from above of the workpiece of FIG. 3A;

FIG. 3C shows a cross sectional view of the workpiece of FIG. 3A afterthe stage has rotated the workpiece 180 degrees from its orientation inFIG. 3A;

FIG. 3D is a perspective view from above of the workpiece of FIG. 3C;

FIG. 3E shows a cross sectional view of a workpiece of FIG. 3A after thestage has rotated the workpiece 90 degrees for its orientation in FIG.3A;

FIG. 3F is a perspective view from above of the workpiece of FIG. 3E;

FIG. 4 is a schematic illustration of the tips of the columns and thenon-tilting stage of a particle beam system similar to the particle beamsystem of FIG. 1;

FIG. 5 is a schematic illustration of the area occupied by the particlebeam system of FIG. 1;

FIG. 6 is a perspective view of a transmission electron microscope (TEM)lamella prior to extraction from a workpiece that has been processed bythe particle beam system of FIG. 1; and

FIG. 7 is a perspective view of a cavity etched into the workpiece ofFIG. 1.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The system 10 illustrated in FIG. 1 with a tilted ion beam column 12 canetch a cavity in a sample to create a vertical cross-section and thenimage the vertical cross-section without tilting the work stage assembly25. FIG. 1 depicts one embodiment of a focused particle beam system 10according to the invention for interacting with a workpiece 30. Thesystem 10 of FIG. 1 includes a tilted ion column 12, a vacuum chamber22, and a work stage assembly 25. The system 10 provides a focusedparticle beam system that can precisely etch and image a cross-sectionof a sample or workpiece 30, e.g., a wafer containing semiconductordevices. The sample is seated within the vacuum chamber 22 and operatedon by a particle beam generated by the tilted column 12 to createcross-sectional images. The images are used to analyze material defectsfound in the wafer, and can provide process engineers with timely datawithout removing the wafer from the production line.

Part of the ion column 12 is located above the vacuum chamber 22, andthe vacuum chamber houses a work stage assembly 25, a sample orworkpiece 30, and a secondary particle detector 28. The system furtherincludes a user control station 50 having a processor 52 and an electrongun 31.

Performance of a Focused-Ion-Beam Implanter with Tilt-Writing Functionby H. Sawaragi et al., Japanese Journal of Applied Physics, Part 1,1989, Vol. 28, No. 10, Pages 2095-2098, incorporated herein byreference, describes an FIB implanter which has an ion optical systemthat can be tilted manually up to 7° without venting the workpiecechamber. This publication states that this system minimizes axial andplanar channeling effects. To control the planar channeling effect, thissystem includes a wafer holder with a sample rotating function. Therotation angle of the wafer can be adjusted from 15° to 25° in 10 steps.However, there remains a need for a system that can etch and image across-section of a workpiece without tilting the work stage.

The illustrated work stage assembly includes a support element 26 and asupport element rotation assembly 24. The support element 26 translatesthe workpiece 30 along a first axis 13, e.g., front and back in thehorizontal plane, and along a second axis 15, e.g., left and right inthe horizontal plane, perpendicular to the first axis 13. The rotationassembly rotates the support assembly around a third axis 17perpendicular to both the first axis 13 and the second axis 15. Therotation assembly 24 can include a 360-degree manually adjustablerotation element 23 and a fast 180-degree hard stop stage rotationelement 27. The operation of the ion column 12, work stage assembly 25,secondary particle detector 28, and optional electron gun 31 can becontrolled by the control station 50.

The illustrated ion column 12 is tilted from vertical so that its axis11 is offset from the third axis 17. In other words, the ion column axis11 forms an acute angle 35 with the third axis 17 (the vertical axis inthis case). In the illustrated embodiment, the angle 35 is forty-fivedegrees. The electron gun 31 can also be tilted from vertical so thatits axis 21 forms an acute angle 36 with the third axis 17. In theillustrated embodiment, the electron gun-third axis angle 36 isforty-five degrees. Further, the ion column axis 11 forms a firstvertical plane with the third axis 17 and the electron gun axis 21 formsa second vertical plane with the third axis 17. In a preferredembodiment, the first plane is substantially perpendicular to the secondplane. This configuration is advantageous because the workpiece can beetched and a vertical cross-section can be imaged without rotating theworkpiece about the third axis 17, and, in the case where the targetpoints of the ion column 12 and of the electron gun 31 are substantiallycoincident, without translating the workpiece in the plane defined bythe first axis 13 and the second axis 15.

Workpieces or samples, such as wafers containing semiconductor devices,can contain features having aspect ratios of 15:1. With reference toFIG. 7, at leas a portion 71 of a structure or feature is contained in avertical cross-section 72 of the workpiece 30. The height 73 of theexposed portion 71 of the structure can be fifteen times the depth orbreadth of the structure. If the cross-section is not sufficientlyvertical, i.e., perpendicular to the plane defined by the workpiece, thestructures of interest may not be accurately reflected in thecross-section. Thus, in order to accurately assess the dimensions of astructure, the cross-section should be sufficiently vertical such thatan individual structure's aspect ratio is likely to be accuratelyreflected in the cross-section. The ability to etch and to image across-section of a workpiece without tilting the work stage is nowdescribed.

As noted above, the system 10 illustrated in FIG. 1 with a tilted ionbeam column 12 can etch a cavity in a sample to create a verticalcross-section and then image the cross-section without tilting the workstage assembly 25. Etching and imaging a cross-section without tiltingthe work stage is accomplished using the system illustrated in FIG. 1 byrotating the workpiece 30 about the third axis 17, as illustrated inFIGS. 3A-3E and as described below. A focused ion beam system with atilted ion beam column 12 etches a cavity 70 with slanted walls 74 andwith vertical walls 72, as shown in FIGS. 3A and 3B. Vertical walls arewalls that are substantially parallel to the third axis 17.

Subsequent to the etching of the cavity 70, the work stage assembly 25rotates the workpiece 30 about the third axis 17. If the work stageassembly 25 rotates the workpiece 30 one hundred and eighty degrees, thefocused ion beam impinges on the slanted wall 74 at substantially normalincidence, i.e., the beam 20 is perpendicular to the slanted wall 74, asshown in FIGS. 3C and 3D. However, if the work stage assembly 25 rotatesthe workpiece 30 ninety degrees about the third axis 17, as shown inFIGS. 3E and 3F, the beam 20 impinges on a vertical wall 72, i.e., avertical cross-section of the workpiece. Thus, the tilted focused ionbeam 20 can etch and image a vertical cross-section of a workpiecewithout tilting the work stage assembly 25 such the work stage assemblyaxis is offset from the third axis 17. In addition, if the electroncolumn and the ion column are located in substantially perpendicularplanes, as described above, the ion beam can etch the workpiece as shownin FIG. 3A, and without rotating the workpiece about the third axis 17,the electron beam can image the vertical wall 72 of the cavity 70. Thesystems and methods according to the invention provide many advantagesas are now discussed.

The work stage assembly is much smaller when it does not include a tiltassembly. A smaller stage assembly results in a smaller footprint, shownschematically in FIG. 5, for the particle beam system. A smallerfootprint results in considerable savings because cleanroom fabricationspace is expensive.

The FIB working distance is improved. In a previous configuration with afocused ion beam oriented normal to the workpiece and an electron beamoffset with respect to the normal, one could not achieve concurrentworking distances that optimized the characteristics, e.g., resolutionand current density, of the ion and electron beams because the workstage and the tip of the ion column and the tip of the electron columnphysically interfere with each other. However, as shown in FIG. 4, byoffsetting the ion column 12 from the normal or third axis 17, both theion column and the electron column 31 can get closer to the workpiece30. For example, a 5 nm, 50 KeV focused ion beam column and an Amrayelectron column, model 3800, each with a 45 degree wafer view, canconcurrently have more optimal working distances of about 10 mm andabout 5 mm, respectively. Such concurrent optimized working distancescontrast with concurrent non-optimized working distances of 16 mm withnormal wafer view for the FIB column and 20 mm with a 60 degree waferview for the electron column in a Micrion 9500IL focused ion beam systemwith a tilting stage.

Furthermore, as shown in FIG. 4, the focused ion beam 12 can betiltable, i.e., the ion focusing optics, 79 can be offset from the thirdaxis, 17.

The particle beam system according to the invention is also more stablebecause the system does not have a tilting stage. The system is morestable because removing the stage tilting mechanism makes the systemmore resistant to low frequency vibration and eliminates gravity sag.

Low frequency vibration can occur when a massive object, such as atilting work stage assembly, is supported by two bearings and heldsteady with an object that behaves like a spring. Thus, a stage that isfixed so that it can not tilt, eliminates a potential source of lowfrequency vibration. Low frequency vibration reduction allows forincreased imaging resolution.

Further when a large work stage assembly is tilted, gravity can bendsome of the components of the work stage assembly and the workpiece.Such bending is termed gravity sag. Because the work stage assembly ismore stable, manufacturers can include a laser interferometer to assistin the determination of the position of the workpiece. Laserinterferometry requires that the laser beams used to perform theinterferometry precisely maintain their spatial relationship.Consequently, the components that direct the laser beams used in theinterferometer must also precisely maintain their spatial relationship.Since at least one of the components that direct the laser beams used inthe interferometer is located on the work stage, the performance of alaser interferometer improves with the reduction of work stage vibrationand with the reduction of gravity sag.

In addition, the configuration of the particle beam system of thepresent invention creates access to the workpiece for other elements.Such elements could include an optical microscope for top-down wafernavigation, a full range of gas injection nozzles including a highvolume "beehive" gas concentrator (described below), or a second FIBcolumn. One advantage of including an optical microscope for top-downwafer navigation is that it provides the focused particle beam systemthe ability to control the location of the surface of the workpiece 30along the third axis 17. The system maintains such control by adjustingthe position of the work stage 25 along the third axis 17 so as tomaintain the surface of the workpiece in focus when viewed through theoptical microscope. By controlling the position of the surface of theworkpiece 30 along the third axis, the system insures that the focusedparticle beam 12 is interacting with a desired location on the surfaceof the workpiece 30.

Further, the configuration of the particle beam system of the presentinvention makes it possible to create a transmission electron microscope(TEM) sample or lamella of relatively uniform thickness. With referenceto FIGS. 1 and 6, in order to create such a lamella, the system etches afirst cavity 90, translates the workpiece 30 and/or deflects theparticle beam, and etches a second cavity 92 in selected proximity tothe first cavity 90 so as to produce a TEM sample wall or lamella 86separating the two cavities. The lamella can have a first side 91 facingthe first cavity and a second side 93 facing the second cavity. Bybombarding the second side of the TEM lamella with electrons from theelectron source 31 and monitoring the change in secondary particleemission from the lamella while etching the second cavity 92, the systemcan monitor the thickness of the lamella 86.

As will be seen from the above description, the system 10 depicted inFIG. 1 provides a system for creating cross-sectional images tofacilitate the analysis of material defects found in the wafer, and canprovide process engineers with timely data without removing the waferfrom the production line.

FIG. 2 depicts an alternative embodiment of a focused particle beamsystem 10 according to the invention for interacting with a workpiece30. The system 10 of FIG. 2 includes an ion column 12, a vacuum chamber22, an optional reactant material delivery system 34 and user controlstation 50. The system 10 provides a focused particle beam system thatcan precisely mill and image a sample 30, e.g., a wafer containingsemiconductor devices. The sample 30 is seated within the vacuum chamber22 and operated on by a particle beam generated by the column 12 tocreate cross-sectional images and analyze material defects found in thewafer.

The ion column 12 includes an ion source 14, an extraction electrode 16,a focusing element 18, deflection elements 19, and a focused ion beam20. The ion column 12 sits above the vacuum chamber 22, and the vacuumchamber 22 houses a work stage assembly 25, a platform 26, a sample 30,a secondary particle detector 28 and a charge neutralization element 32.As further depicted by FIG. 2, the optional reactant material deliverysystem 34 includes a reservoir 36, a manometer 40, a motorized valveelement 42, and delivery conduit 44. The user control station 50includes the processor 52, a pattern recognition element 54, the memoryelement 56, a display element 60, a scan generator element 62, and dwellregisters 64.

It will be apparent to one of ordinary skill in the art, that the system10 depicted in FIG. 2 includes a conventional focused ion beam (FIB)system with an ion column 12 disposed above a vacuum chamber 22 thatincludes an optional reactant material delivery system 34 for providingreactant materials to the interior of chamber 22. As will be understoodby one of ordinary skill in the art, the depicted ion column 12 is aschematic representation of one ion column suitable for practice withthe invention. The depicted ion column 12 includes an ion source 14 thatcan be a liquid metal ion source (LMIS) such as a gallium ion source, orcan be a gas field ion source (GFIS) such as a helium ion source. Theion source 14 sits above the extraction electrode 16. The extractionelectrode 16 generates sufficient electric field to draw an ion streamfrom the ion source 14. The ion stream travels past focusing element 18,that can be conventional electro-optical lenses that focus the ionstream to the finely-focused beam 20. As further depicted, the ioncolumn 12 includes the deflection elements 19 that can deflect the ionbeam 20 to scan across the surface of the sample 30.

Similarly, the evacuation chamber 22 can be a conventional evacuationchamber that includes a work stage assembly 25 for supporting aworkpiece 30. The work stage assembly 25 includes a support element 26and a support element rotation assembly 24. The support element 26 iscapable of translation along a first axis and along a second axisperpendicular to the first axis. The rotation assembly 24 is adapted forrotating the support element 26 about a third axis perpendicular to boththe first axis and the second axis. Thus, the work stage assembly 25provides control of the displacement of the workpiece being operated onby the system 10.

Similarly, evacuation chamber 22 includes a charge neutralizationelement 32, such as an electron gun, and further includes a secondaryparticle detector 28 for detecting secondary particles, such aselectrons, ions, or any other particles suitable for generating an imageof the workpiece. Any vacuum chamber 22 as schematically depicted hereincan be practiced with the present invention, including the vacuumchamber sold with the ion beam workstation sold by Micrion Corporationof Peabody, Mass.

Similarly, the optional reactant material delivery system 34 can be anyconventional reactant material delivery system suitable for deliveringreactant material such as precursor gases into the interior of thevacuum chamber 22, and more particularly into the chamber 22 andproximate to the surface of the workpiece. The reactant materialdelivery system 34 can deliver materials to the surface of the sample 30to enhance the etching of material from the surface or alternatively, todeposit material on the surface of the sample.

The depicted reactant material 34 includes a reservoir 36 that couplesin fluid communication with the fluid delivery conduit 44 that has adistal portion formed as a nozzle for delivering reactant materials tothe surface of the workpiece. The depicted reactant delivery system 34includes a manometer 40 coupled to conduit 44 for measuring the deliverypressure within conduit 44 of any reactant materials being delivered tothe surface of the workpiece 30. Manometer 40 further couples to themotorized valve element 42. The motorized valve element 44 isselectively controllable for increasing or reducing the flow of reactantmaterials of reservoir 36 through fluid delivery conduit 44. Thearrangement of the manometer 40 and motorized valve 42 depicted in FIG.2 forms a feedback control system wherein the manometer 40 measures thedelivery pressure within conduit 44 and selectively controls themotorized valve 42 to increase or decrease the flow of reactant materialto thereby maintain a select delivery pressure.

Improved gas delivery systems are provided by coupling to the distal endof a gas nozzle, a shroud-type concentrator that has an interior axialpassage. The gas nozzle provides a flow of reactant material throughthat passage. Concurrently, a particle beam can pass through the samepassage to a substrate surface being processed. This concentrator istermed a "beehive" gas concentrator.

The interior passage of the concentrator has a partially flaredconfiguration that is understood to provide a transition from theconfined fluid passage within the delivery system to the workpiece sitebeing processed. The flared passage in one embodiment includes afrusto-conical shape, and has a least area at the upper aperture of thepassage and a greatest area at an axially-opposed lower aperture. The"beehive" gas concentrator is more fully described in pending U.S.patent application Ser. No. 08/667,966, incorporated herein byreference.

The operation of the ion column 12, charge neutralization element 32,and secondary particle detector 28 are controlled by the control station50. The depicted control station 50 includes a processor element 52 thathas a scan generator element 62 that includes dwell register 64. Theprocessor element 52 couples via a transmission path to a controlelement 58 coupled to the ion beam column 12. The depicted processorelement 52 can be a conventional computer processor element thatincludes a CPU element, a program memory, a data memory, and aninput/output device. One suitable processor element 52 is a IBM RSCWorkstation using a Unix operating system.

As further depicted by FIG. 2, the processor element 52 can connect, viathe input/output device to a scan generator element 62. In oneembodiment, the scan generator element is a circuit card assembly thatconnects to the processor 52 via the processor input/output device. Thecircuit card assembly scan generator element 62 depicted in FIG. 2includes a scan memory for storing data representative of a scanningpattern that can be implemented by system 10 for scanning ion beam 20across the surface of the workpiece 30 to selectively mill, etch orimage the surface of the workpiece 30.

The scan generator board element 62 depicted in FIG. 2 can be aconventional computer memory circuit card having sufficient memory forstoring digital data information representative of locations of featuresof the sample that are to be processed by the particle beam system 10.Typically, a scan generator board suitable for practice with the presentinvention includes a series of memory locations, each of whichcorresponds to a location on the workpiece surface. Each memory locationstores data representative of an X and Y location of the sample andpreferably further has, for each X and Y location, a dwell register forstoring digital data representative of a time for maintaining theparticle beam on the surface of the sample at the location representedby the associated X, Y pair. Accordingly, the dwell register provides amemory location for storing a dwell time for applying the focusedparticle beam to the surface of the sample, to thereby allow control ofthe dose delivered to the workpiece.

It will be apparent to one of ordinary skill in the art of focusedparticle beam processes and systems that the dose delivered to alocation on a workpiece surface can be understood to determine generallythe depth to which material is removed from that location of theworkpiece. Accordingly, the dwell time signal stored in the dwellregister can also be understood as representative of a depth, or Zdimension, for the particle beam milling process. Consequently, theprocessor 52 that couples to such a scan generator board 62 provides amulti-dimensional milling element for generating milling signals thatcan control in three dimensions the etching or imaging process of thefocused particle beam system.

Accordingly, the processor 52 employs the X, Y data maintained by thescan generator board 62 to generate milling signals that are transmittedvia the transmission path 66 to the control element 58 of the ion column12. In the depicted embodiment, the milling signals provide controlelement 58 with information for operating the deflector elements 19 todeflect the focused particle beam for scanning or rasterizing thefocused particle beam across the surface of the workpiece 30, and tomaintain the particle beam at the selected location for a specifieddwell time to provide milling to a selected depth. The surface of theworkpiece 30 generally corresponds to a two-dimensional plane that canbe defined by an orthogonal pair of X and Y axes. A Z axis, that isgenerally understood as extending parallel to the path of the focusedion beam 20 is also generally orthogonal to the plane defined by the Xand Y axis of the surface of the workpiece 30. By controlling thelocation of the particle beam 20 and the period of time for which thebeam 20 impacts against the surface of the workpiece 30, material atselected locations of the workpiece 30 can be removed. Accordingly, thesystem 10 provides multidimensional control of the milling process tothereby allow the particle beam 20 to remove selected portions of theworkpiece surface and form a precise geometry on the workpiece.

Although FIG. 2 depicts an ion column 12 that includes deflectionelements 19 for deflecting an ion beam 20 to scan across the surface ofthe workpiece 30 and thereby direct the focused ion beam to a selectedlocation on the surface of the workpiece 30, it will be apparent to oneof ordinary skill in the art of focused particle beam processing thatany system suitable for directing the focused particle beam to selectlocations of the workpiece surface can be practiced with the invention.For example, in an alternative embodiment, the platform 24 can be movedin an X, or Y space which corresponds to the X, and Y space of themilling process and the milling signals generated by the processor 52can be provided to a stage control system that moves the stage carryingthe workpiece 30 to thereby dispose a selected portion of the workpiecedirectly in the path of the focused particle beam to mill or image theworkpiece 30. Other systems and methods for directing the particle beamcan be practiced with the present invention without departing from thescope thereof.

It will be further be apparent to one of ordinary skill in the art ofparticle beam processes and systems that the depicted scan generatorelement 62 that is illustrated as a circuit card assembly of read/writecomputer memory can alternatively be implemented as software programcode that runs on a computer platform having an accessible data memorythat is configured by the program code to provide storage locations forstoring the data representative of the X and Y locations as well as datarepresentative of the dwell time. Such a modification is well within theart of one of ordinary skill and does not depart from the scope of theinvention.

In this embodiment of the invention, the pattern recognition element 54generates an image of the surface of the portion of the workpiece 30 andprocesses the image to determine the precise position of a feature. Theposition of the workpiece geometry can be represented by a coordinatesignal that can define, in one embodiment, the coordinates of theperiphery of the feature's footprint relative to a predefinedregistration point. The use of predefined registration points, which actas landmarks, is known in the art of ion beam processing for manuallypositioning a workpiece during a preliminary step of a focused particlebeam process. Other systems and methods for initializing the coordinatesystem employed by the pattern recognition system 54 can be practicedwith the present invention without departing from the scope thereof

The system 10 depicted in FIG. 2 includes a pattern recognition system54 that connects via transmission path 48 to the depicted ion column 12,and further couples via transmission path 68 to the secondary particledetector 28 wherein transmission path 68 carries image data to thepattern recognition element 54, and further couples via transmissionpath 46 to the charge neutralization element 32 wherein transmissionpath 46 carries a control signal to the charge neutralization element 32for activating and deactivating the charge neutralizer 32. In thedepicted embodiment, the pattern recognition element 54 further connectsvia a bidirectional bus to the memory element 56 that acts as a computermemory element for storing data representative of known featurepresentations.

In the embodiment depicted in FIG. 2, the pattern recognition system 54employs the focused ion beam column 12 and the secondary particledetector 28 to generate an image of the surface of the workpiece 30.Specifically, the pattern recognition element 54 generates a series ofscanned control signals that are transmitted via transmission path 48 tothe control element 58 of the ion column 12. The scanned control signalsdirect the control element 58 to scan the focused ion beam across the XYplane that defines the surface of the workpiece 30 and particularly toscan the ion beam across the portion of the surface 30 that includes thefeatures of interest. The scanning of the ion beam 20 across theworkpiece surface 30 causes the emission of secondary particles,including secondary electrons and secondary ions. The secondary particledetector 28 detects the omitted secondary particles and provides animage signal 68 to the pattern recognition system 54. The patternrecognition system 54 coordinates the image signal with the scanningsignals that generate deflection signals that apply to the deflectorelements 19 and correlates the image signal with the deflector signalsso that changes in the detected signals are associated with particulardeflection signals amplitudes corresponding to a particular location onthe workpiece surface 30.

The detector 28 may be one of many types such as an electron multiplier,a micro channel plate, a secondary ion mass analyzer, a photon detectoror an energy dispersive detector for detecting X-rays produced as aresult of bombardment of the workpiece with an electron beam. Techniquesare described herein are well known in the art of focused ion beamprocessing and any substitutions, modifications, additions orsubtraction's to the imaging technique can be described herein is deemedto be a scope of the invention. Preferably during the imaging processthe pattern recognition element 54 generates a control signaltransmitted via transmission path 46 to the charge neutralizationelement 32. The charge neutralization element 32 depicted in FIG. 2 isan electron gun element that directs a beam of electrons towards thesurface of the workpiece surface 30. The beam of electrons neutralizes abuilding static electric charge that arises on the workpiece surface 30during the imaging operation. By reducing the built-up electric staticcharge the charge neutralizer reduces the defocusing the ion beam anddeflecting of the ion beam that results from the positive surface chargeon the workpiece 30 that defocuses and deflects the positively chargedion beam 20 scanning across the workpiece surface 30. Accordingly, thecharge neutralizer element 32 allows the system 10 to generate moreprecise images of the workpiece features.

The pattern recognition element 54 stores the image signalrepresentative of the image of the workpiece and a computer memory thatforms part of the pattern recognition element 54. The patternrecognition element 54 includes a pattern recognition processor such asone manufactured and sold by the Cognex Corporation of Needham, Mass.Further, the pattern recognition system 54 can supply the image signalof the workpiece surface to the display 60 for displaying the workpiecefeatures to the system user.

The pattern recognition element 54 analyzes the image signal stored inthe recognition element computer memory. The analysis performed by thepattern recognition element 54 is described in pending U.S. patentapplication Ser. No. 08/635,063, herein incorporated by reference.

As will be seen from the above description, the system 10 depicted inFIG. 2 provides a system for milling and imaging a workpiece feature.The system 10 automatically identifies the location and geometry of aworkpiece feature and, generates from the location and geometricinformation a set of milling signals that direct the focused particlebeam to mill the workpiece. Thus, the system 10 can create a workpiecefeature that has the precise geometry suitable for imaging and processanalysis. One such operation, etching and imaging of a cross-section ofa workpiece, was described above in connection with FIGS. 3A-3F.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are officially attained. Sincecertain changes may be made in the above constructions without departingfrom the scope of the invention, it is intended that all mattercontained in the above description and shown in the accompanyingdrawings be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended tocover all generic and specific features of the invention describedherein, and all statements of the scope of the invention which as amatter of language might be said to fall therebetween.

Having described the invention, what is claimed as new and secure byletters patent is:
 1. A particle beam system for interacting with aworkpiece, such system comprising:a housing for housing the workpiece,and means for processing the workpiece contained in said housing, saidmeans includinga work stage assembly adapted a) for supporting theworkpiece, b) for translating the workpiece along a first axis, c) fortranslating the workpiece along a second axis perpendicular to the firstaxis, and d) for rotating the workpiece about a third axis perpendicularto both the first axis and the second axis, said work stage assemblyhaving a work stage axis substantially parallel to the third axis, and afirst particle beam source for etching and imaging the workpiece, saidfirst particle beam source having a first particle beam source axisoriented to form an acute angle with the third axis, such that theparticle beam system can etch and can image a vertical cross-section ofthe workpiece without offsetting the work stage axis from the thirdaxis.
 2. A particle beam system according to claim 1 wherein said firstparticle beam source is oriented so that the first particle beam sourceaxis forms an angle of greater than seven degrees and less than ninetydegrees with the third axis.
 3. A particle beam system of claim 1,wherein the first particle beam source is oriented such that the firstparticle beam axis forms an angle of about forty-five degrees with thethird axis.
 4. A particle beam system according to claim 1 furthercomprisinga second particle beam source for interacting with theworkpiece and located in selected proximity to said first particle beamsource, the second particle beam source having a second particle beamaxis oriented substantially parallel to the third axis.
 5. A particlebeam system according to claim 1 further comprisinga second particlebeam source for interacting with the workpiece and located in selectedproximity to said first particle beam source, the second particle beamsource having a second particle beam axis offset relative to the thirdaxis.
 6. A particle beam system according to claim 1 furthercomprisingan electron beam source for interacting with the workpiece andlocated in selected proximity to the first particle beam source, theelectron beam source having an electron beam axis and being oriented sothat the electron beam axis is selectively offset relative to the thirdaxis.
 7. A particle beam system according to claim 6 wherein the firstparticle beam axis and the electron beam axis each form an angle ofabout forty-five degrees with the third axis, andwherein the firstparticle beam axis and the third axis form a first plane and theelectron beam axis and the third axis form a second plane orientedsubstantially perpendicular to the first plane.
 8. The apparatusaccording to claim 1 further comprisinga laser interferometer means forassisting in the determination of the position of the workpiece andlocated within said housing in selected proximity to said work stageassembly, said laser interferometer means includinga laser source fordirecting laser radiation along a path in a first direction, a beamsplitter located in the path of said laser radiation from said lasersource and for transmitting a first part of said laser radiation alongsaid first direction, and for reflecting a second part of said laserradiation along a second direction, at least one reference mirror forreflecting back to said beam splitter the first transmitted part of saidlaser radiation, and at least one test mirror for reflecting back tosaid beam splitter the second reflected part of said laser radiation andlocated on said work stage assembly, such that the beam splittercombines the first transmitted part and the second reflected part of thelaser radiation to form interference fringes that assist in thedetermination of the position of the workpiece.
 9. A particle beamsystem according to claim 1 further comprisinga gas injection sourcehaving a gas injection nozzle located in selected proximity to theworkpiece.
 10. A particle beam system according to claim 1 wherein thework stage assembly rotates about the third axis more than twenty-fivedegrees.
 11. A particle beam system according to claim 1 furthercomprisingan optical microscope for interacting with the workpiece, saidoptical microscope having an optical microscope axis orientedsubstantially parallel to the third axis.
 12. A particle beam system forinteracting with a workpiece, said system comprising:a housing forhousing the workpiece, and means for processing the workpiece containedin said housing, said means includinga work stage assembly adapted a)for supporting a workpiece, b) for translating the workpiece along afirst axis, c) for translating the workpiece along a second axisperpendicular to the first axis, and d) for rotating the workpiece abouta third axis perpendicular to both the first axis and the second axis,said work stage means having a work stage axis substantially parallel tothe third axis, and a first particle beam source for etching and imagingthe workpiece supported by the work stage assembly, the first particlebeam source having a first particle beam axis, the first particle beamsource being tiltable from a first position, with the first particlebeam axis substantially parallel to the third axis, to a secondposition, with the first particle beam axis forming an acute angle withthe third axis, such that the particle beam system can etch and image avertical cross-section of the workpiece without offsetting the workstage axis from the third axis.
 13. A particle beam system forinteracting with a workpiece comprising:a housing for housing theworkpiece, and focused particle beam processing apparatus arranged toprocess the workpiece contained in said housing, said focused particlebeam apparatus includinga work stage assembly for supporting a workpieceand for orienting the workpiece in a plane, said work stage assemblyhavinga support element adapted for translating the workpiece along afirst axis, and for translating the workpiece along a second axisperpendicular to the first axis, the support element having a first sideand a second side, and a positioning assembly coupled to the first sideof the support element and adapted for rotating the support element andthe workpiece about a third axis perpendicular to both the first axisand the second axis, such that the workpiece can be seated on the secondside of the support element and translated in a plane and rotated aboutthe third axis normal to that plane, and a first particle beam sourcefor etching and imaging the workpiece supported by the work stageassembly, the first particle beam source having a first particle beamaxis, the first particle beam source being tiltable from a firstposition with the first particle beam axis substantially parallel to thethird axis, to a second position with the first particle beam axisforming an acute angle with the third axis, such that the particle beamsystem can etch and image a vertical cross-section of the workpiecewithout tilting the work stage axis relative to the third axis.